Expedited module unloading for kernel modules that execute read-copy update callback processing code

Abstract

A technique for expediting the unloading of an operating system kernel module that executes read-copy update (RCU) callback processing code in a computing system having one or more processors. According to embodiments of the disclosed technique, an RCU callback is enqueued so that it can be processed by the kernel module's callback processing code following completion of a grace period in which each of the one or more processors has passed through a quiescent state. An expediting operation is performed to expedite processing of the RCU callback. The RCU callback is then processed and the kernel module is unloaded.

Description

BACKGROUND[0001]1. Field[0002]The present disclosure relates to computer systems and methods in which data resources are shared among data consumers while preserving data integrity and consistency relative to each consumer. More particularly, the disclosure concerns an implementation of a mutual exclusion mechanism known as “read-copy update” in a computing environment wherein loadable modules contain code that is used to process read-copy update callbacks.[0003]2. Description of the Prior Art[0004]By way of background, read-copy update (also known as “RCU”) is a mutual exclusion technique that permits shared data to be accessed for reading without the use of locks, writes to shared memory, memory barriers, atomic instructions, or other computationally expensive synchronization mechanisms, while still permitting the data to be updated (modify, delete, insert, etc.) concurrently. The technique is well suited to both uniprocessor and multiprocessor computing environments wherein the n...

AI Technical Summary

Problems solved by technology

By way of example, a network routing table that is updated at most once every few minutes but searched many thousands of times per second is a case where read-side lock acquisition would be quite burdensome.

Other techniques for tracking blocked readers may also be used, but tend to require more read-side overhead than the current blocked task list method.

If the module containing the callback function code is unloaded before a pending callback that requires such code can be invoked, problems will arise when an attempt is made to implement the callback function because its code is no longer part of the running kernel.

Unfortunately, the rcu_barrier( ) primitive can delay module unloading due to the latency associated with waiting for the end of a current RCU grace period and for all prior RCU callbacks to be invoked.

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